Single-blow pneumatic percussive tool

ABSTRACT

A single-blow pneumatic percussive tool includes a hollow cylindrical casing (1) having inlet and outlet ports (2, 3). A hammer piston (4) mounted in the casing (1) divides the interior space of the casing (1) into lower and upper chambers (5,6). A working tool (7) is mounted in the casing (1) on the side of the lower chamber (5). A handle (9) having passages and an air distribution device (8) is mounted in the upper part of the casing (1). A sleeve (12) with ports (13) is mounted on the casing (1) to define a space (14) therewith. An air distribution sleeve (15) is axially biased by a spring mounted in the space (14). The outlet ports (3) of the casing (1) are aligned with the ports (13) of the sleeve (12). The air distribution sleeve (15) has radial ports and recesses (17) which are aligned with the radial ports ( 16) on both surfaces of the air distribution sleeve (15). At least one passage (18) is made in the hammer piston (47) which is biased by spring on the side of the lower chamber (5).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to pneumatic percussive tools used in theconstruction and mining industries, mechanical engineering andmetallurgy, and more specifically, it deals with single-blow pneumaticpercussive tools.

2. Description of the Prior Art

Pneumatic percussive tools, in particular, pneumatic hammers are usedfor marking, center-popping, riveting, marking-out and gate trimming.Depending on a specific application, the pneumatic hammer has a workingtool such as a stamp, center punch or chisel. The working tool ismounted in a casing having an interior space and inlet and outlet ports.The interior space of the casing accmmodates a hammer piston definingworking chambers in the interior space. An energy carrier is gaseousfluid under pressure which is supplied to the tool from a portable orstationary compressor along a flexible hose. During operation of thetool, the hammer piston axially reciprocates under the action ofcompressed air alternately admitted to the working chambers through theair distribution device to impart a blow to the end face of the workingtool at every working cycle. The working tool performs work under theaction of blows whereby, depending on the type of the working tool,marking, center-popping, trimming or riveting takes place.

Since operations performed using such tools are effected with the directparticipation of the operator, stringent requirements are imposed upontheir reliability (durability) and operating conditions.

Known in the art is a single-blow pneumatic percussive tool (cf. USSRInventor's Certificate No. 706239, Int.Cl. B 25 D 9/04), comprising ahollow cylindrical casing having inlet and outlet ports accommodating ahammer piston having an opening and dividing the interior space of thecasing into upper and lower chambers, and a spring-biased working toolhaving a head in the form of a valve mounted on the side of the lowerchamber for establishing communication thereof with atmosphere when thehammer piston moves downwards.

For starting the tool, i.e. for causing the hammer piston to move down,it is necessary that the lower chamber communicate with atmosphere. Inthis tool such communication is possible when the working tool ispressed against the workpiece surface so that the head in the form of avalve provides for communication of the lower chamber with atmosphere.However, big effort is needed on the part of the operator for startingthe tool so that operating conditions are complicated and impact energydecreases.

Known in the art is a single-blow pneumatic percussive tool (cf. USSRInventor's Certificate No. 1027026, Int. Cl. B 25 D 9/04, comprising ahollow cylindrical casing having inlet and outlet ports andaccommodating a hammer piston which divides the interior space of thecasing into upper and lower working chambers, a working tool, a sleevewith ports mounted in the casing for movement relative thereto, and astarting device in the form of a spring-biased valve mounted on the sideof the lower chamber.

The lower chamber should communicate with atmosphere to effect thehammer piston movement downwards. In this tool, this is achieved bypressing against the working tool so that the latter is caused to moveuntil it bears against the sleeve. However, in orer to move the sleeveto such an extent that the lower chamber might communicate withatmosphere through the sleeve ports and the tool might be started, theforce applied to the working tool must be great enough. Since the toolis started by the operator, great forces should be applied thuscomplicating operating conditions and lowering impact energy of thetool.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide a single-blowpneumatic percussive tool in which impact energy of a single blow isincreased by modifying direction of flow of gaseous fluid under pressurein the interior space of the casing.

The invention substantially resides in a single-blow pneumaticpercussive tool comprising a hollow cylindrical casing with inlet andoutlet ports accommodating a reciprocatable hammer piston which dividesthe interior space of the casing into lower and upper chambers, aworking tool mounted in the casing on the side of the lower chamber, anair distribution device mounted in a handle installed on the upper partof the casing and having passages for admission of gaseous fluid underpressure to the interior space of the casing, a sleeve with portsdefining with the casing and intermediate space which communicates atregular intervals with the lower chamber through the outlet ports foradmission of gaseous fluid under pressure. According to the inventionthe tool comprises an air distribution sleeve which is axially biased bya spring and has radial ports and recesses aligned with the radial portson both surfaces of the air distribution sleeve which is mounted forreciprocations in the intermediate space alternately communicating withone passage for admission of gaseous fluid under pressure and withatmosphere, and the outlet ports of the casing are aligned with theports of a sleeve rigidly mounted outside the casing, the outlet portsbeing covered by the sleeve when the air distribution sleeve is in theupper position and establish communication of the lower chamber withatmosphere through the radial ports when the air distribution sleeve isin the lower position, the lower and upper chambers communicating witheach other through at least one passage made in the hammer piston whichis biased by a spring on the side of the lower chamber.

This construction of the tool makes it possible to increase impactenergy owing to the maximum possible speed of evacuation of the lowerchamber from gaseous fluid under pressure and to improve operatingconditions of the tool because only a slight force should be applied forstarting the tool.

The outlet ports of the casing are preferably made in the form oftransverse slits.

This arrangement of the outlet ports of the casing makes it possible toincrease impact energy of the tool owing to the maximum possible speedof their opening which minimizes the opening time.

The grooves of the air distrubution sleeve are preferably of a widthwhich is greater than the width of the outlet ports.

This arrangement of the grooves makes it possible to increase impactenergy of the tool owing to full opening of the outlet ports and,respectively, rapid evacuation of the lower chamber from gaseous fluidunder pressure during the workstroke of the hammer piston.

The air distribution sleeve is preferably provided with a retainer forretaining it in the uppermost position, the sleeve being subsequentlyreleasable under the action of gaseous fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to a specificembodiment shown in the accompanying drawings, in which:

FIG. 1 schematically shows a single-blow pneumatic percussive toolaccording to the invention during the return stroke of the hammerpiston, in longitudinal section;

FIG. 2 shows a single-blow pneumatic percussive tool at the moment whenthe hammer piston imparts a blow to the working tool, in longitudinalsection; and

FIG. 3 is a sectional view taken along line III--III in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A single-blow pneumatic percussive tool shown in FIGS. 1, 2 comprises ahollow cylindrical casing 1 having inlet ports 2 and outlet ports 3accommodating a reciprocatable hammer piston 4 which divides theinterior space of the casing 1 into a lower chamber 5 and an upperchamber 6. A working tool 7 is mounted in the casing 1 on the side ofthe lower chamber 5. A handle 9 is mounted in the upper part of thecasing 1 and accommodates an air distribution device 8 and has passages10, 11 for the admission of gaseous fluid under pressure to the interiorspace of the casing 1. A sleeve 12 is rigidly mounted on the casing 1and has ports 13, the sleeve defining with the casing 1 an intermediatespace 14 in which an air distribution sleeve 15 is mounted forreciprocation, the air distribution sleeve being axially biased by aspring and having radial ports 16 and recesses 17. The outlet ports 3 ofthe casing 1 are aligned with the ports 13 of the sleeve 12. Therecesses 17 are aligned with the radial ports 16 on both surfaces of theair distribution sleeve 15. The width of the recess 17 is greater thanthe width of the outlet ports 3. The hammmer piston 4 has one passage 18for establishing communication between the lower chamber 5 and upperchamber 6. In another embodiment there may be two, three and even morepassages in the hammer piston. Moreover, a spring 19 is mounted in theinterior space of the casing 1 for cooperation with the hammer piston 4on the side of the lower chamber 5, and a shock-absorber 20 engageablewith the hammer piston 4 is provided on the side of the upper chamber 6.A groove 21 is made in the air distribution sleeve 15 for cooperationwith a ball retainer 22 for retaining the air distribution sleeve 15 inthe upper position and for its subsequent release under the action ofgaseous fluid in the intermediate space 14. The casing 1, on the side ofthe lower chamber, accommodates a spring 23 cooperating with the airdistribution sleeve 15 and a cover 24 for retaining the working tool 7in the casing 1. The handle 9 has a passage 25 for communicating theintermediate space 14 with atmosphere.

The single-blow pneumatic percussive tool functions in the followingmanner.

Gaseous fluid under pressure is admitted through a socket pipe of thehandle 9 (FIG. 1), passage 11 and inlet ports 2 to the upper chamber 6and, via the passage 18 of the hammer piston 4, to the lower chamber 5.The air distribution sleeve 15 is in the uppermost position under theaction of the spring 23, and the intermediate space 14 communicates withatmosphere through the air distribution device 8 and passage 25 whilethe hammer piston 4 is held in the uppermost position by the spring 19,the position of the hammer piston being defined by the shock-absorber20. When the air distribution device 8 is moved to the uppermostposition (FIG. 2), the passage 25 is shut-off, and gaseous fluid underpressure is admitted through the passage 10 and air distribution device8 to the intermediate space 14 to act upon the end face of the airdistribution sleeve 15 which is retained by engagement of the groove 21and ball retainer 22. As soon as pressure in the intermediate space 14reaches a preset value, the air distribution sleeve 15 is released andit will move under the action of gaseous fluid under pressure towardsthe lowermost position defined by the cover 24 to compress the spring23. The lower chamber 5 communicates with atmosphere through the outletports 3, recesses 17, radial ports 16 and ports 13 which are in registrywith one another, and gaseous fluid under pressure will be abruptlydischarged from the lower chamber into atmosphere. The width of therecesses 17 is greater than the width of the outlet ports 3 becauseotherwise inadequate discharge of gaseous fluid under pressure from thelower chamber would result in the formation of a cushion in the lowerchamber 5 during the workstroke of the hammer pistion 4 thus loweringimpact energy. Owing to a pressure difference between the lower andupper chambers 5 and 6, the hammer piston 4 will move under the actionof gaseous fluid under pressure on the side of the upper chamber 6 tocompress the spring 19 towards the lowermost position and to impart atthe end of travel a blow to the working tool 7 which is in engagementwith the workpiece surface to perform useful work.

After the admission of gaseous fluid under pressure to the intermediatespace 14 is interrupted (FIG. 1) the latter will connect to atmospherethrough the air distribution device 8 and passage 25, and the airdistribution sleeve 15 will move towards the upper position under theaction of the spring 23. As soon as the air distribution sleeve 15covers with its wall the outlet ports 3, pressure in the lower chamber 5will become equal to pressure in the upper chamber 6 owing to thepassage 18 of the hammer piston 4, and the hammer piston will be movedby the spring 19 to the uppermost position defined by the shock-absorber20. The air distribution sleeve 15 will move to the uppermost positionand will be retained in this position by means of the groove 21 and ballretainer 22.

In comparison with prior art types of single-blow pneumatic percussivetools, the tool according to the invention makes it possible to effectan abrupt discharge of gaseous fluid under pressure from the lowerchamber and ensures a low force for starting the tool.

These advantages result in an increase of impact energy by 7-10% andimprove labour conditions.

The invention may be most advantageously used in tools designed formarking, center-popping, riveting, marking-out and gate trimming.

The invention may also be used in apparatuses for mining working rooftrimming, for demolishing concrete, making holes and performing otheroperations in the construction industry.

We claim:
 1. A single-blow pneumatic percussive tool comprising a hollowcylindrical casing (1) with inlet and outlet ports (2, 3) accommodatinga reciprocatable hammer piston (4) which divides the interior space ofthe casing (1) into lower and upper chambers (5, 6), a working tool (7)mounted in the casing (1) on the side of the lower chamber (5) an airdistribution device (8) mounted in a handle (9) installed on the upperpart of the casing (1) and having passages (10, 11) for admission ofgaseous fluid under pressure to the interior space of the casing (1), asleeve (12) with ports (13) defining with the casing (1) an intermediatespace (14) which communicates at regular intervals with the lowerchamber (5) through the outlet ports (3) for admission of gaseous fluidunder pressure an air distribution sleeve (15) which is axially biasedby a spring; and has radial ports (16) and recesses (17) aligned withthe radial ports (16) on both surfaces of the air distribution sleeve(15) which is mounted for reciprocations in the intermediate space (14)alternately communicating with one passage (10) for admission of gaseousfluid under pressure and with atmosphere, and the outlet ports (3) ofthe casing (1) are aligned with the ports (13) of the sleeve (12)rigidly mounted outside the casing (1) the outlet ports (3) beingcovered by the sleeve (15) when the air distribution sleeve (15) is inthe upper position and establish communication of the lower chamber (5)with atmosphere through the radial ports (16) when the air distributionsleeve (15) is in the lower position, the lower and upper chambers (5,6)communicating with each other through at least one passage (18) made inthe hammer piston (4) which is biased by a spring on the side of thelower chamber (5).
 2. A tool according to claim 1, wherein the outletports (3) of the casing (1) are in the form of transverse slits,
 3. Atool according to claim 1, wherein the recesses of the air distributionsleeve (15) are of a width which is greater than the width of the outletports (3).
 4. A tool according to claim 1, wherein the air distributionsleeve (15) is provided with a retainer (22) for retaining the sleeve inthe uppermost position for subsequent release thereof under the actionof gaseous fluid.